As a characteristic value governing wiping performance of a wiper device, an error angle indicating an angle between a wiper blade (hereinafter, abbreviated as “blade” as needed) and a windshield. In general, the error angle is set to an angle slightly shifted in such a direction that the blade is dragged from 0 (right angle between a wiping surface and blade) at an intermediate position between blade upper and lower reversing positions. In this case, an inclining direction of the blade in a wiper operation forward path and that of the blade in a wiper operation return path are opposite to each other (error angle setting directions are opposite to each other). It follows that the inclining direction of the blade is reversed after reversal operation, and thereafter the wiping operation is performed in such a way that the blade is dragged.